This invention relates to an exhaust silencer system for a two-cycle engine and more particularly to an improved arrangement for silencing the exhaust gases of a ported two-cycle engine.
Although two-cycle engines are widely used for a variety of applications because of their simplicity and their high power output per displacement, there are some disadvantages with such engines. One problem particularly prevalent with two-cycle engines is the noise associated with their exhaust. This noise is a result of several factors, one of which is the fact that the exhaust gases are discharged to the atmosphere during each rotation of the crankshaft as opposed to every other crankshaft rotation as with a four-cycle engine. In addition, the porting of the engine causes the exhaust gases to emanate from the exhaust port quite rapidly and this itself gives rise to significant silencing problems.
In addition, two-cycle engines are normally employed in relatively confined applications such as outboard motors, motorcycles or the like wherein the provision of a large and complex exhaust silencing system is not possible. As a result, there is some objection to the use of two-cycle engines even in these applications due to the difficulty in silencing.
It has been proposed to silence the exhaust gases of a two-cycle engine by providing an expansion chamber into which the exhaust gases can expand before the exhaust port is opened. However, the previously proposed constructions have been such that the communicating passageway that communicates the cylinder with the expansion chamber is not fully opened before the exhaust port is opened. As a result, the full utilization of the expansion chamber cannot be employed.
Furthermore, the prior art systems have had the disadvantage that the communication passageway is open after the exhaust port is closed and when the piston is still traveling toward its top dead center position. As a result, these type of devices tend to reduce the effective compression ratio of the engine and, accordingly, its power output.
In addition to the aforenoted defects, those systems which have been previously proposed have necessitated the formation of the expansion chamber either in the cylinder head in whole or in part and also have not afforded an opportunity to provide any cooling for the expansion chamber.
It is, therefore, a principal object of this invention to provide an improved exhaust silencer system for a two-cycle engine.
It is a further object of this invention to provide an exhaust silencer system for a two-cycle engine that includes an expansion chamber and a communicating port that communicates the expansion chamber with the cylinder but which will not have the defects of the prior art constructions.
It is a further object of this invention to provide an improved exhaust silencing system utilizing an expansion chamber that communicates with the cylinder but wherein the compression ratio of the engine is not adversely affected.
It is a further object of this invention to provide an exhaust silencer for a two-cycle engine employing an expansion chamber and wherein the expansion chamber communicates completely with the cylinder before the exhaust port opens.
It is a further object of this invention to provide a silencing system for a two-cycle engine including an expansion chamber and a valve that can be tailored to control the expansion chamber so as to not adversely affect other conditions of the engine and also to achieve maximum silencing.
It is a still further object of this invention to provide an expansion chamber silencing device for a two-cycle engine wherein the expansion chamber is cooled so as to assist in silencing.